Conventionally, magnetic measurement in studies of physical properties has been performed with two parameters; i.e., temperature and magnetic field. However, in recent years, more and more active studies have been performed on physical properties in which, through introduction of pressure as a new parameter, magnetic functionally is investigated in a complex, extreme environment; i.e., high magnetic field, very low temperature, and high pressure.
FIG. 4 is a view showing a typical piston cylinder-type high-pressure generating device. A sample, and a liquid pressure medium for transmitting pressure to the sample and maintaining hydrostatic pressure acting thereon are enclosed in a capsule, and the capsule is disposed in a pressure chamber formed between a pair of pistons disposed to face each other. A pair of piston bearers are axially positioned by means of clamp nuts engaged with opposite end portions of a cylinder portion. Pressure is applied to the pair of piston bearers by use of, for example, oil pressure applied through center openings of the clamp nuts. The piston bearers transmit the pressure to the pressure chamber, in which the capsule is disposed, via the pistons.
Since the high-pressure generating device is used in a wide temperature range from cryogenic temperature to room temperature, the high-pressure generating device must be excellent in heat conductively. Furthermore, in order to allow detection of a very weak magnetic signal of a measurement sample, the high-pressure generating device must be formed of a non-magnetic material. Therefore, the material used to fabricate the high-pressure generating device is limited to alloys (CuBe, CuTi) containing copper as a main component. In consideration of measurement by use of a superconductive quantum interference device (SQUID) flux meter, which is used globally, the outer diameter of the cylindrical high-pressure generating device must be 8.6 mm or less. Moreover, in order to enable measurement of a sample, such as an antiferromagnetic substance, which exhibits a weak magnetic response only, the high-pressure generating device must secure an effective sample space of about 10 mm3.
FIG. 5 is a view used for describing measurement by making use of a superconductive quantum interference device (SQUID) flux meter (see Patent Document 1). A change in magnetic flux detected by a superconductive pickup coil is detected via a superconductive quantum interference device SQUID, which serves as a transformer. An AC coil for generating an alternating magnetic field is provided outside the superconductive pickup coil, and a magnet for generating an external magnetic field is provided outside the AC coil so as to generate a stable magnetic field and provide a magnetic shield. An object of this magnet is to provide an enhanced magnetic shield function and a very stable steady magnetic filed, to thereby enable reduction of influence of magnetic noise by means of hardware. A sample whose magnetization is to be measured is located in the vicinity of the superconductive pickup coil. The superconductive pickup coil, the superconductive quantum interference device SQUID, and the external magnetic field generating magnet are cooled to a superconductive state by a refrigerator.
The magnetization of the sample is measured through DC measurement or AC measurement. In the DC measurement, the sample is moved over a distance of about 4 cm, from a position about 6 mm below the lowest coil portion of the detection coil dividedly wound to have three coil portions, to a position about 6 mm above the highest coil portion thereof, and the position dependency of an output voltage signal at that time is analyzed. In AC measurement, Fourier analysis is performed on the difference between an output voltage signal obtained at a position about 6 mm below the lowest coil portion and that obtained at the position of the center coil portion. In either measurement method, since the sample moves through the detection coil system, the entire structure of the high-pressure generating device is strongly desired to be formed of the same material.
In the case where the entire device is formed of copper beryllium (CuBe) under such a restriction, the device can generate only a relatively low pressure of 8 to 9 kbar. In the case where piston portions which transmit load to the sample are formed of hard ceramic, through use of a worm-gear-type pressurizing device, the maximum generation pressure reaches 15 kbar (see Non-patent Document 1). However, sensitivity of magnetic measurement lowers.
Also, conventionally, a support jig for preventing expansion of a cylinder portion has been indispensable. The diameter ratio of the cylinder portion (the ratio of the outer diameter to the inner diameter) is, for example, 8.50/2.60=3.27. Therefore, in order to generate a high pressure exceeding 10 kbar, a support jig for preventing expansion of the cell is essential, and only a system in which a pressurizing device is integrated with such a high-pressure generating device can generate a pressure up to 15 kbar.
Under such circumstances, there has been long awaited the appearance of a device in which the mechanical strength of CuBe is maximally utilized so as to enable the entire device to be formed of CuBe, and which can generate a pressure higher than 15 kbar, while maintaining satisfactory magnetic detection accuracy. Also, since the exemplified device has a cylinder length of 80 mm, which is very long as compared with its internal diameter of 2.6 mm, an operation of inserting a sample-enclosing capsule is difficult.